Resin-treated mercerized fibers and products thereof

ABSTRACT

This invention relates to the process of manufacture of resin treated mercerized cellulose fibers and fibrous products prepared therefrom and is directed particularly to a method of improving permeability and bulking properties and reducing water retention value (WRV) of a conventional high permeability bulk pulp. The invention also includes the improved cellulose fibers, cellulosic sheet materials containing said fibers, and products therefrom (such as automotive oil and air filters).

This application claims, under 35 U.S.C. § 119, the benefit of thefiling date of U.S. application Ser. No. 60/060,278 filed Sep. 29, 1997,incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a process for manufacture of resin-treated,mercerized cellulose fibers and fibrous products prepared therefrom andis directed particularly to a method of improving permeability andbulking properties and reducing the water retention value (WRV) of amercerized, high porosity bulk pulp. The invention also includes theimproved cellulose fibers, cellulosic sheet materials containing saidfibers, and products manufactured therefrom (such as automotive oil andair filters).

BACKGROUND OF THE INVENTION

Cellulose fibers currently available in the market do not exhibit alldesired properties for use in certain applications. For example, in themanufacture of automotive oil and air filters, it is desirable that thefibers exhibit reduced WRV and produce structures (e.g., filters) withhigh permeability and bulk with adequate sheet strength. However, onecommercially available fiber produces structures with high permeabilityand bulk but does not have adequate sheet strength. Another commerciallyavailable fiber produces structures with higher permeability and bulk,but is brittle and loses permeability under conventional refiningconditions. Another commercially available fiber produces structureswith high permeability and bulk, but has an undesirably high WRV. Thus,there is a need in the art for improved cellulose fibers having reducedWRV that can produce structures with high permeability and bulk.

Attempts have been made to improve conventional manufacturing processesto obtain cellulose fibers of desired properties. For example, Shaw etal. describe in U.S. Pat. No. 3,819,470 that swellability, which is aresult of water absorption, can be reduced by treating fibers with asubstantive polymeric compound and fluff-drying. Adjusting parametersfor improving quality of cellulose fibers are described in U.S. Pat. No:3,756,913 to Wodka; U.S. Pat. No: 4,361,463 to Lindberg et al.; U.S.Pat. No: 4,853,086 to Graef; U.S. Pat. No: 2,926,116 to Keim et al.; andU.S. Pat. Nos: 5,200,036 and 5,015,245 to Noda. All patents (andreferences therein) cited herein are incorporated by reference. However,cellulose fibers that exhibit the desired properties as described hereinhave not been previously reported.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a process flow diagram of one embodiment of the presentinvention.

FIG. 2 is a graph showing comparative permeability between commerciallyavailable mercerized cellulose fibers and fibers treated according toone embodiment of the invention.

FIG. 3 is a graph showing comparative WRV data between commerciallyavailable mercerized cellulose fibers and fibers treated according toone embodiment of the invention.

FIG. 4 is a graph showing comparative bulk data between commerciallyavailable mercerized cellulose fibers and fibers treated according toone embodiment of the invention.

FIG. 5 is a graph showing comparative drying rate data between refinedblends of commercially available mercerized cellulose fibers withnon-mercerized fibers and a blend containing fibers treated according toone embodiment of the invention.

FIG. 6 is a graph comparing the tensile values at various permeabilitylevels for refined blends of conventional mercerized cellulose fibersand unmercerized cellulose fibers, refined blends of conventional resintreated fibers and unmercerized cellulose fibers, and values for refinedblends of fibers treated according to one embodiment of the inventionand unmercerized cellulose fibers.

FIG. 7 is a graph comparing tensile values at various permeabilitylevels between refined blends of conventional mercerized cellulosefibers and unmercerized cellulose fibers, refined blends of conventionalresin-treated fibers and unmercerized cellulose fibers, and refinedblends of fibers treated according to one embodiment of the inventionand unmercerized cellulose fibers.

SUMMARY OF THE INVENTION

It has now been surprisingly discovered that fibers (and fiberstructures produced thereof) with improved permeability and bulkingproperties and reduced water retention value (WRV) may be obtained in aprocess that combines mercerization of cellulose fibers and treatmentwith a low molecular weight, water dispersible polymer. The combinationof these two steps results in cellulose fibers with low WRV (waterretention value), and good tolerance to refining (non-brittleness) thatprovide exceptional properties to fiber structures or products such ashigh permeability and high bulk.

The invention thus relates to a process of manufacture of resin-treated,mercerized cellulose fibers and fibrous products prepared therefromwhich have improved properties in comparison to a conventional highporosity bulk pulp.

In another aspect, the invention relates to resin-treated, mercerizedcellulose fibers and fibrous products having high permeability, highbulk, low WRV, and good tolerance to refining.

In yet another aspect, the present invention relates to high flowfilters such as automotive oil and air filters prepared from theresin-treated, mercerized cellulose fibers of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a process for manufacturing resin-treatedmercerized cellulose fibers and fibrous products prepared therefrom. Theprocess includes the steps of treating cellulose fibers with mercerizingstrength caustic, for example 18% NaOH (or another swelling agent),followed by treatment with a low molecular weight, water dispersiblepolymer, for example a polyamide epichlorohydrin adduct (PAE). A processflow diagram of one embodiment of the present method is illustrated inFIG. 1.

The process of the invention may be used with any cellulosic fibersource and mixtures thereof to improve permeability, refinability, andWRV. Examples of preferred fibers are SSK (Southern Softwood Kraft), NSK(Northern Softwood Kraft), HK (Tropical Hardwood Kraft), cotton lintercellulose, NSS (Northern Softwood Sulfite), and SSS (Southern SoftwoodSulfites).

Methods for mercerizing cellulose pulp are generally known in the art.For example, pulp can be mercerized according to any suitable method ofcaustic treatment at low, medium and high consistency. Generally, pulpis treated under agitation with caustic at a concentration of 80grams/liter (g/l) or higher, at a temperature of about 20° C. or higher.The preferred caustic is sodium hydroxide. Potassium hydroxide may alsobe used. During this treatment, the cellulose fibers swell considerablyand a portion of the hemicellulose associated with the cellulose isdissolved. The pulp is subsequently neutralized and washed. Theresulting fibers are no longer straight but are bent, curled, swollenand more porous. The step of mercerization and the effect of caustic onthe cellulose fiber is further described in, for example, Rydholm, ed;Pulping Processes (Interscience Publishers, 1965) and Ott, Spurlin andGrafflin, eds; Cellulose and Cellulose Derivatives, Vol V, Part I(Interscience Publishers, 1954) which are incorporated herein byreference.

Fibers can be mercerized to different degrees before they are treatedwith resin. It is within the skill of those of ordinary skill in the artto optimize the degree of mercerization. For example, Frazierpermeability of an unpressed TAPPI handsheet may be used as an indicatorof a desired degree of mercerization. Mercerized cellulose is also knownas “hydrate cellulose” and the two terms are used here interchangeably.

Resin treatments generally known in the art can be used in combinationwith the mercerization step of the invention. Any low molecular weight,water dispersible polymer may be used in the present method. Forexample, low molecular weight polymer resins that polymerize in thepresence of heat, such as urea and melamine formaldehydes, can be used.In a preferred embodiment of the invention, a cationic wet-strengthresin such as polyamide epichlorohydrin adduct (PAE) is used.

The amount of resin that is used in the invention is generally low, forexample between 0.1 and 0.6 wt solids % of dry pulp, compared to theamount of resin generally employed for producing resin-treated bulkingfibers as taught in U.S. Pat. No. 3,756,913 to Wodka and U.S. Pat. No.5,399,240 to Graef. In another embodiment, the amount of resin may be upto 1.0 wt solids % of dry pulp. Such low concentrations are sufficientonly when the cellulose fibers are pre-mercerized. Low resinconcentrations have the advantage of preventing formation ofnon-repulpable knots and pills which can be a serious problem withcertain commercially available resin-treated fibers. However, resin canalso be applied in a concentration of up to 1.5% or more. The preferredconcentration of resin will depend on the resin used and the degree ofmercerization achieved. One skilled in the art can determine a suitableconcentration based on the following considerations. The amount of resinused should improve permeability, WRV and bulk of the pre-mercerizedfiber while somewhat maintaining its strength relative to itspermeability. Also, the concentration of resin used should be low enoughto avoid formation of non-repulpable knots and pills in a sheetcontaining resin treated pulp after it is refined.

In one preferred embodiment, the method of the invention includes thefollowing steps:

1. Feeding pulp of 94 to 90% starting consistency to a mercerizationstage where mercerizing strength caustic is introduced to produce a lowconsistency slurry (consistency is defined as wt % fiber in water);

2. washing the resulting caustic containing pulp using a countercurrentwasher to recover some strong caustic and provide washed, mercerizedpulp;

3. introducing to the pulp a polyamide epichlorohydrin adduct (PAE) (acationic wet strength resin), at 0.1 to 1.5% wt % of dry pulp indilution water which also contains sulfuric acid to adjust the pulp pHto about 5.5 to 6.5;

4a. drying the pulp by pressing the pulp to about 45 to 50% consistencyand subjecting it to fluffing to individualize the fibers which may haveclumped together; and heating to about 300° F. in a tunnel dryer to drythe pulp and cure the (PAE) resin; or

4b. drying the pulp using a pulp drying machine to produce a sheetedproduct with sufficient heat to cure the resin.

According to another aspect of the invention, fibers may bepre-mercerized, formed into sheets or bulk-dried, then repulped andtreated with resin, and subsequently re-dried in a bulk or sheet form.

The resin-treated, mercerized fibers prepared according to the method ofthe present invention have increased permeability (CFM/ft² of astandardized handsheet), decreased water retention value and increasedbulk. Furthermore, resin-treated mercerized fibers can be made at alower cost than non-resin treated, mercerized fibers of equalpermeability properties because the amount of caustic used can bereduced in some cases by as much as 40% while the beaten, unpressedTAPPI handsheet permeability can be restored to its original level bythe addition of about 0.4% PAE resin based on bone dry (b.d.) pulpweight.

The fibers prepared according to the present invention can be used in anumber of ways as will be recognized by those skilled in the art. Onepreferred use is in the automotive industry for manufacturing air andoil filters. Such filters can be made by methods well known in the art.Generally, the mercerized, resin-treated fibers of the present inventioncan be blended with other commercially available fibers, and filterpaper made using conventional machinery such as, for example, a lowconsistency inclined wire paper machine. The fibers of the presentinvention can also be used to prepare bulking tissue for use, forexample, for making diapers.

The improved properties of cellulose fibers prepared according to thisinvention are illustrated in the following non-limiting examples.

EXAMPLES Example 1

To determine properties of the cellulose fibers prepared according tothe present invention, test materials listed in Table 1 were prepared.

Experimental Fiber 1, was prepared as follows. Never-dried southernsoftwood kraft pulp was mercerized in a low consistency process asdescribed above, washed, then treated with 0.6% Kymene 557H wet-strengthresin (PAE) solids on a dry pulp basis, centrifuged, air dried to 50 to55% consistency, fluffed and placed in a static oven at 105° C.overnight.

Kymene 557H resin was obtained from Hercules Inc., Wilmington, DE.Kymene 557H, a registered trademark of Hercules, is a polyamideepichlorohydrin (PAE) resin which is prepared by reacting adipic acidand diethylene triamine monomers to form a polymer which is then reactedwith epichlorohydrin to generate a final product which is a complexmixture of polymers.

Experimental Fiber 2, was prepared as follows. A sheet-dried, mercerizedsouthern softwood kraft pulp was repulped in water to low consistencyand treated with 0.6% Kymene 557H solids on a dry pulp basis,centrifuged, fluffed, dried in a through-air tunnel dryer at 275° F. for5 to 8 minutes and then baled.

Experimental Fiber 3, was prepared as follows. Never-dried southernsoftwood kraft pulp was mercerized in a low consistency process, washed,then treated with 1.0% Kymene 557H solids on a dry pulp basis, formedinto a sheet, wet pressed using a felt, dried on a dryer train toapproximately 0-3% moisture, then placed in a static oven at 105° C.overnight.

Experimental Fiber 4, was prepared as follows. Never dried southernsoftwood kraft pulp was mercerized in a high consistency process,washed, then treated with 0.4% Kymene 557H solids on a dry pulp basis,pressed to 40 to 45% consistency, fluffed, and dried in a through-airtunnel dryer at 300° F. for 5 to 8 minutes and then baled.

Experimental Fiber 5, was prepared as follows. Foley Fluff, acommercially available southern softwood kraft pulp (available fromBuckeye Technologies, Inc., Memphis, TN) was repulped in water,centrifuged, mercerized in a low consistency process, washed, thentreated with 1.0% Kymene 557H solids on a dry pulp basis, centrifuged,air dried to 50 to 55% consistency, fluffed, and placed in a through-airdryer at 300° F. for 10 minutes.

Experimental Fiber 6, was prepared as follows. A bulk-dried, mercerizedsouthern softwood kraft pulp was repulped in water and treated with 1.0%Kymene 557H solids on a dry pulp basis, centrifuged, fluffed, and placedin a static oven at 105° C. for 8 hours.

Properties of experimental fibers were compared with properties of fourcontrol fibers. Control Fiber 1 was sheet-dried, mercerized SSK pulp,Control Fiber 2 was bulk-dried, mercerized SSK, Control Fiber 3 wasnon-mercerized, sheet-dried SSK and Control Fiber 4 was non-mercerized,resin-treated bulk-dried SSK.

TABLE I Unpressed Tappi Handsheet Properties Refined PermeabilityUnrefined Bulk Unrefined (cfm/ft2) Tensile Refined Tensile (g/in) (cc/g)WRV (%) Material Description Permeability 500 revs 1000 revs (g/in) 500revs 1000 revs 500 revs 500 revs 1000 revs Control Fiber 1 308 311 31592 182 297 6.6 103.2 109.9 (Sheet-dried, mercerized SSK) Control Fiber 2456 368 352 50 231 376 7 107.4 114.6 (Bulk-dried, mercerized SSK)Control Fiber 3 70 64 51 1034 2283 3284 3.9 118.1 132.1 (Sheet-driedSSK) Control Fiber 4 479 291 250 10 101 191 8.1 67.3 69.4 (Bulk-dried,resin-treated SSK) Experimental Fiber 1 753 622 501 9 14 33 7.8 96.8100.8 (Low cons. mercerized SSK Resin treated-Bulk dried) ExperimentalFiber 2 >757 465 410 7 24 51 7.5 91 96.1 (Repulped merc.SSK Resintreated - Bulk dried) Experimental Fiber 3 586 434 404 9 29 71 6.2 — —(Low cons.merc. SSK- Resin treated - Sheet dried) Experimental Fiber 4717 351 326 16 100 218 6.8 105.7 111.1 (High cons.merc. SSK - Resintreated-Bulk dried) Experimental Fiber 5 >757 504 455 10 18 25 7.8 87.994.6 (Dried SSK low cons. mercerized Resin treated - Bulk dried)Experimental Fiber 6 >757 478 439 12 31 54 7.5 73.5 77.1 (High cons.merc. SSK - Resin treated-Bulk Dried)

Handsheets were made from each fiber according to TAPPI Method T205except that a 0.5% consistency slurry was used during the disintegrationstep and the handsheets were not pressed. Samples were refined accordingto TAPPI Method T248 before unpressed handsheets were made.

The following properties were measured on the unpressed handsheets:unrefined and refined permeability (cfm/ft²), and unrefined and refinedtensile values (g/in). WRV (%) measurements were made on fibers.

Unrefined and refined permeability and tensile values were determinedusing standard procedures generally known in the art. Tensile valueswere determined using TAPPI Method T494. Permeability was determinedusing an air permeability tester. Specifically, four handsheets perexperimental fiber were tested in the air permeability tester. For eachhandsheet a pressure drop of one half inches of water was establishedacross the handsheet and air flow through the sheet was measured by thepressure drop across an orifice indicated on a vertical manometer. Theaverage manometer reading was converted to air permeability usingconversion tables.

Water retention values were determined using the following procedure.Briefly, dry samples were subdivided to ensure that a slurry be easilyobtained upon wetting. Wet samples that were partially dewatered wereweighed. Samples were subjected to swelling for 16 to 24 hours. Swollensamples were centrifuged at 1500 g. The moist, centrifuged samples wereweighed, dried at 105±2° C. and reweighed. The water retained in thesamples after centrifugation was primarily retained due to swelling.Generally, some surface or occluded water remains after centrifugationand, therefore, to ensure comparable WR values, standardized conditionswere maintained.

A detailed step-by-step procedure for determining WRV is outlined below.

Day 1

1. Shredding (by hand) a dry sample to increase the surface area as muchas possible (if the sample is wet proceeding to step 2);

2. shaking vigorously 1 to 2 grams of the sample in a 250 ml Erlenmeyerflask with 100 ml deionized H₂O;

3. condition weighing flasks in an oven at 105±2° C. overnight.

Day 2

1. Removing weighing flasks from oven and placing in desiccator to coolfor one hour;

2. weighing flasks before centrifuging;

3. filling funnels with samples and placing into centrifuge tubes;adjusting centrifuge speed to ensure that required acceleration isattained after 1 minute; centrifuging for 10 minutes;

4. allowing centrifuge to coast to a stop and then removing samples;

5. rapidly transferring centrifuged samples into a tared weighingbottles and reweighing;

6. placing samples in an oven at 105±2° C. overnight.

Day 3

1. Removing samples from oven, cooling in a desiccator for one hour andreweighing.

The above procedure is described in “The Determination of the WaterRetention Capacity (Swelling Value) of Pulps”, Theodor Hopner, GeorgJayme and Johannes C. Ulrich, Das Papier, Vol. 9, No. 19/20, 1955, pp.476-482.

The WRV values were calculated according to the following formula.${WRV} = \frac{\left( {{{Weight}\quad {of}\quad {wet}\quad {centrifuged}{\quad \quad}{sample}} - \quad {{weight}\quad {of}{\quad \quad}{dry}\quad {sample}}} \right) \times 100}{{Weight}{\quad \quad}{of}\quad {dry}\quad {sample}}$

The rpm required for an acceleration of 1500 g was calculated asfollows: ${rpm} = {299.05\frac{\sqrt{1500}}{r}}$

r being the radius of the centrifuge measured from the middle of theaxis of rotation to the constriction in the centrifuge tube for the stemof the funnel tube.

The results of this experiment are represented in Table 1.

Table 1 shows that Experimental Fibers 1, 2, 4, 5 and 6 each hadincreased porosity at a lower WRV in comparison to Control Fiber 2.Experimental Fibers 1, 2, 5, and 6 had increased porosity at a lower WRVin comparison to Control Fiber 1.

Experimental Fibers 1, 2, 5 and 6 had increased bulk compared tomercerized fibers such as Control Fiber 1 and Control Fiber 2 which werenot treated with resin. The increased bulk remained within an acceptablerange, in that the filter sheet was deemed likely to still fit withinthe existing filter canister dimensions, which is important for filterpaper production. Generally, increased bulk is desirable because itincreases filter capacity. However, pore size should remain withincurrent limits set by the filtration manufacturers, since an increase inpore size causes a decrease in filter efficiency.

Example 2

Mercerized SSK fibers were treated with 1.0% Kymene 557H based on bonedry (b.d.) pulp weight as described in Example 1. Permeability, bulk andWRV of the treated fibers were compared with permeability, bulk and WRVof SSK fibers prepared according to a conventional method (i.e., withmercerization but without the addition of polymer) after subjecting thefibers to a refining step at several different amounts or degrees ofrefining (expressed in a total number of revolutions [“rev”]). Resultsare represented in FIGS. 2, 3, and 4.

FIG. 2 shows that fibers prepared according to the method of theinvention have higher permeability compared to fibers prepared accordingto conventional methods over a range of refining from 0 to 2500 rev.

FIG. 3 shows that fibers prepared according to the method of theinvention have lower WRV values compared to fibers prepared according toconventional methods over a range of refining of from 0 to 2500 rev.

FIG. 4 shows that fibers prepared according to the method of theinvention have higher bulk than the fibers prepared according toconventional methods over a range of refining of from 0 to 2500 rev.

Example 3

Filter paper manufacturers generally achieve target paper properties byblending different fibers. To determine the properties of blendscontaining fibers of the present invention, the following tests wereperformed.

A blend of 65% Experimental Fiber 4 and 35% Control Fiber 3 wasprepared. Control Fiber 3 is a non-mercerized sheet-dried, southernsoftwood kraft pulp. Two control blends were prepared: a blend of 65%Control Fiber 2 and 35% Control Fiber 3 and a blend of 75% Control Fiber1 and 25% Control Fiber 3. These control blends are typical for furnishblends run in the filter paper industry. The blends were refined using aPFI mill as described in TAPPI method T-248 to a target porosity of100-115 cfm/ft² for a 100 g/m² sheet. The refining conditions wereintended to simulate conical refining of a furnish blend in a filtermanufacturing plant. Unpressed handsheets were made and tested forpermeability, tensile value, density, WRV and pore size. The handsheetswere weighing about 100 g/m² which is a typical filter sheet weight.Table 2 shows the test results.

Table 2 shows that unpressed handsheets containing a blend withExperimental Fiber 4 had similar pore size to the blends containingControl Fiber 2 and Control Fiber 1.

TABLE 2 35% Control Fiber 3 35% Control 25% Control 65% Fiber 3 Fiber 3Experimental 65% Control 75% Control Fiber #4 Fiber 2 Fiber 1 BlendBlend Blend Permeability (cfm/ft 2) 117 111 111 Tensile (gm/in) 712 1202763 Density (gm/cc) 0.190 0188 0.189 WRV (%) 105.5 104.2 101.0 Pore Size(microns) 31.69 32.81 33.92

The above fiber blends were also tested for drying rate and the resultsare represented in FIG. 5 and Table 3. FIG. 5 shows that the blend of65% Experimental Fiber 4 and 35% Control Fiber 3 dried at approximatelythe same rate as the blend of 75% Control Fiber 1 and 25% Control Fiber3. The blend of 65% Experimental Fiber 4 and 35% Control Fiber 3 driedsignificantly faster than the blend of 65% Control Fiber 2 and 35%Control Fiber 3. For example, as evident from Table 3, a blendcontaining Experimental Fiber 4 contained 3.3% moisture at Dryer 4 whilethe Control Fiber 2 blend contained 8.14% moisture. Those skilled in theart will appreciate that a difference of nearly 5% moisture issignificant, particularly in a filter manufacturing plant where thespeed of a paper machine line for sheeting a refined furnish blend isbased on the moisture of the sheet at the rewinding reel. It is wellknown that the sheet moisture must be controlled and should not exceed5.0%. Under such conditions, even a 0.1% moisture reduction issignificant.

TABLE 3 65% Exper. 65% Control 75% Control Fiber 4 Fiber 2 Fiber 1 %sheet moisture % sheet moisture % sheet moisture Couch (hand 63.97 67.1567 rolled) #1 Vac (high) 63.00 64.45 64.64 #2 Vac (high) 62.52 64.3264.08 Dryer 1 47.30 50.00 47.01 Dryer 2 33.66 36.76 32.23 Dryer 3 18.0022.52 17.07 Dryer 4 3.30 8.14 3.77 Dryer 5 0.00 0.98 0.00 Dryer 6 0.000.49 0.49 Dryer 7 0.00 0.00 0.00 Dryer 8 0.00 0.00 0.00 Dryer 9 0.000.00 0.00 Dryer 10 0.00 0.00 0.00 Bone Dry wt. 2.05 2.03 2.04 Revs. 350350 350 (pfl mll 1)

Example 4

To determine the properties of refined blends containing fibers of thepresent invention, and determine their suitability for filtermanufacturing, the following tests were performed.

This experiment was conducted in two stages. In the first stage, anexperimental blend of 65% Experimental Fiber 4 and 35% Control Fiber 3and a control blend of 65% Control Fiber 2 and 35% Control Fiber 3 wereprepared. In the second stage, a blend of 65% Control Fiber 4 and 35%Control Fiber 3, and a second control blend of 65% Control Fiber 2 and35% Control Fiber 3 were prepared. The control blends were typical offurnish blends run in the filter paper industry. Samples of the blendswere refined using a PFI mill as described in TAPPI method T-248 over arange of revolutions. Unpressed handsheets (weighing 60 g/m²) were madeand tested for blend Frazier porosity and tensile value for each degreeof refining. The test was repeated using the blends as described, exceptthat a single stage experiment was performed. The results are presentedin FIGS. 6 (two-stage test) and 7.

Example 5

To demonstrate the improved permeability and bulking properties of theinvention, the following samples were mercerized and resin treated:Northern Softwood Kraft, Eucalyptus, Southern Sulfite, Grade 512 CottonLinter, and Southern Softwood Kraft.

To mercerize the fiber samples, each was repulped to 250 g b.d. wt. ofthe fiber in 18% NaOH and permitted to steep for 1 hour. The NaOHsolution was then drained off and the sample was washed with water andneutralized with H₂SO₄ (adjusted to pH 6-7). The pulp was then slurriedat 3.75% consistency.

To resin-treat each mercerized sample, 1% Kymene® 557H wet-strengthresin (PAE) solids on a dry pulp basis was added to the slurry andallowed to remain for 20 minutes. For example, 10 g of the 12.5% solidsKymene (as received from the manufacturer) could be used to treat a 125g sample. The slurry was centrifuged to approximately 50% consistencyand adjusted by air drying. The treated pulp was fluffed through a twostage lab disintegrator. Fluffed fiber was then cured overnight in a laboven at 105° C.

The permeability and bulk properties of each mercerized sample wascompared before and after resin treatment. In each sample, Frazierpermeability improved after resin treatment by approximately 1.8 to 2.5times more than after mercerization alone, while bulk propertiesincreased by as much as 18% (Eucalyptus). The improved permeability andincrease in bulk of the resin-treated fibers permits better filtrationcapacity of filter paper made from the fibers.

TABLE 4 After Mercerization After Mercerization and Resin TreatmentTreatment Frazier Bulk Frazier Bulk FIBER SPECIES (CFM/ft2) (cc/g)(CFM/ft2) (cc/g) Southern Softwood Kraft 389 7.7 697 8.2 NorthernSoftwood Kraft 175 7.4 345 8.2 Southern Softwood Sulfite 308 7.3 610 8Grade 512 Cotton Linter 424 7.1 >757 7.3 Eucalyptus 70 5.9 172 6.9

Example 6

This Example demonstrates the improved bulking, permeability, andtensile properties of a fibrous product treated with resin and millrefined according to methods of the present invention. MercerizedSouthern Softwood Kraft was treated with various resins. Control Fiber 1was mercerized Southern Softwood Kraft without resin treatment.Mercerization was performed as described in Example 1, except thatresin-treated fibers were dried after mercerization in the presentExample.

To resin treat the sample, three 200 g b.d. wt. portions of themercerized fiber were repulped and slurried at 3.75% consistency. Toprepare experimental samples, 1% Kymene 557H solids (PAE) (based on b.d.fiber weight) was added to the first slurry portion, 1% Parez 607(modified melamine resin; Cytec Industries Inc., W. Paterson, N.J.)(based on b.d. fiber weight) was added to the second slurry portion, and10% of a melamine-formaldehyde resin (based on b.d. fiber weight), as itwas received from the manufacturer (BASF, Ludwigshafen, Germany), wasadded to the third slurry portion. Each batch portion was allowed tostay in the resin-containing slurry for 20 minutes. The slurry wascentrifuged to approximately 50% consistency and adjusted by air drying.The treated pulp was fluffed through a two stage laboratorydisintegrator, and cured in a laboratory oven at 105° C. overnight. Theresin treated fiber samples were then tested for permeability bulkproperties and tensile strength under mill refined conditions andwithout the conditions.

The data in Table 5 reveal that permeability and bulking properties wereeach improved by treating mercerized fiber samples with resin. In theabsence of mill refining (i.e., Revs=0), the Frazier and bulk valueswere visibly improved for resin-treated samples than for ControlFiber 1. Both the 1% modified melamine and 10% melamine-formaldehyderesin-treated samples demonstrated excellent permeability, havingFrazier values of 757 CFM/ft² or greater, and bulking properties rangingfrom 7.9 to 8.3 cc/g. The 1% PAE treated sample also exhibited markedimprovements in these values over Control Fiber 1, which had much lowerpermeability and bulking properties at about 300 CFM/ft² and 6.2 cc/g,respectively.

As expected, PFI mill refining of the samples resulted in lower valuesfor permeability and bulking than without refining, however these valueswere generally improved over values determined for Control Fiber 1 underthe same conditions. Therefore, depending on the extent of PFI millrefining necessary and the permeability and bulking properties desired,one skilled in the art can select from a variety of resins taught by theinvention to improve the properties in the fiber selected.

TABLE 5 Resin Evaluation Table Fra- Ten- PFI Mill zier sile Resinapplied to Sam- Refined (CFM/ (g/ Bulk Control Fiber 1 ple (Revs) ft²)inch) (cc/g) None 1A 0 298 84 6.2 ″ 1B 0 301 83 6.1 ″ 1C 0 304 77 6.3 ″2A 500 360 96 6.8 ″ 2B 500 360 97 7.1 ″ 2C 500 360 109 6.8 ″ 3A 1000 352142 6.8 ″ 3B 1000 352 131 6.9 ″ 3C 1000 358 112 6.8 ″ 4A 1500 343 1806.9 ″ 4B 1500 349 157 6.6 ″ 4C 1500 346 157 6.9 1% Modified MelamineResin 5A 0 >757 13 8.1 ″ 5B 0 >757 12 7.8 ″ 5C 0 >757 12 8.1 ″ 6A 500383 39 7.4 ″ 6B 500 398 37 7.2 ″ 6C 500 410 37 7.4 ″ 7A 1000 349 99 7.1″ 7B 1000 371 87 7 ″ 7C 1000 363 89 7.1 ″ 8A 1500 328 210 7 ″ 8B 1500346 192 7.2 ″ 8C 1500 332 207 7.1 1% Polyamide 9A 0 550 18 8Epichlorohydrin Resin 1% Polyamide 9B 0 565 16 7.8 Epichlorohydrin Resin1% Polyamide 9C 0 568 18 7.8 Epichlorohydrin Resin 1% Polyamide 10A 500366 78 7.1 Epichlorohydrin Resin 1% Polyamide 10B 500 378 69 7.2Epichlorohydrin Resin 1% Polyamide 10C 500 347 70 7.2 EpichlorohydrinResin 1% Polyamide 11A 1000 331 131 7 Epichlorohydrin Resin 1% Polyamide11B 1000 347 122 7 Epichlorohydrin Resin 1% Polyamide 11C 1000 342 1167.1 Epichlorohydrin Resin 1% Polyamide 12A 1500 319 220 6.8Epichlorohydrin Resin 1% Polyamide 12B 1500 325 215 6.9 EpichlorohydrinResin 1% Polyamide 12C 1500 328 211 6.9 Epichlorohydrin Resin 10%Melamine-Formaldehyde 13A 0 757 13 8.3 Resin 10% Melamine-Formaldehyde13B 0 757 13 8.3 Resin 10% Melamine-Formaldehyde 13C 0 757 12 7.9 Resin10% Melamine-Formaldehyde 14A 500 497 22 7.8 Resin 10%Melamine-Formaldehyde 14B 500 505 20 8 Resin 10% Melamine-Formaldehyde14C 500 508 18 8 Resin 10% Melamine-Formaldehyde 15A 1000 425 38 7.3Resin 10% Melamine-Formaldehyde 15B 1000 413 39 7.7 Resin 10%Melamine-Formaldehyde 15C 1000 422 45 7.5 Resin 10%Melamine-Formaldehyde 16A 1500 383 88 7.2 Resin 10%Melamine-Formaldehyde 16B 1500 398 74 7.2 Resin 10%Melamine-Formaldehyde 16C 1500 395 73 7.3 Resin

What is claimed is:
 1. A method for preparing resin-treated mercerizedfibers comprising the steps of: (a) mercerizing cellulose pulp; (b)neutralizing said mercerized cellulose pulp; (c) treating saidmercerized pulp with a low molecular weight, water dispersible polymerresin, said resin present in an amount between about 0.1 and about 10%solids per dry weight of said cellulose pulp; (d) recoveringresin-treated, mercerized cellulose fibers from said pulp; and (e)drying and curing the recovered resin treated mercerized cellulosefibers to obtain individualized, cured fibers.
 2. The method of claim 1,wherein said drying and curing step is accomplished by heating saidfibers.
 3. The method of claim 2, wherein said heating takes place atabout 300° F.
 4. The method of claim 1, wherein said low molecularweight polymer resin is a cationic, wet strength resin.
 5. The method ofclaim 1, wherein said resin is selected from the group consisting ofpolyamide epichlorohydrin adduct, urea, melamine formaldehyde, andmixtures thereof.
 6. The method of claim 5, wherein said resin ispolyamide epichlorohydrin adduct.
 7. The method of claim 4, wherein saidresin is present in an amount of between about 0.1 and about 1.5% solidsper dry weight of said cellulose pulp.
 8. The method of claim 1, whereinsaid cellulose pulp is selected from the group consisting of southernsoftwood kraft, northern softwood kraft, tropical hardwood kraft,northern softwood sulfite, southern softwood sulfite, or cotton lintercellulose.
 9. The method of claim 1, wherein said mercerizing stepincludes treatment of said pulp with a swelling agent.
 10. The method ofclaim 9, wherein said swelling agent is selected from the groupconsisting of sodium hydroxide, potassium hydroxide, and mixturesthereof.
 11. The method of claim 10, wherein said swelling agent issodium hydroxide.
 12. The method of claim 9, wherein said swelling agentis present at a concentration of at least about 80 grams/liter.
 13. Themethod of claim 9, wherein said mercerizing step is performed at atemperature of at least 20° C.
 14. Individualized cellulose fiberstreated with a low molecular weight, water dispersible polymer resin,wherein said resin is present in the amount of between about 0.1 andabout 10% solids per dry weight of said cellulose fiber.
 15. The fiberof claim 14, wherein said resin is selected from the group consisting ofpolyamide epichlorohydrin adduct, urea or melamine formaldehyde.
 16. Thefiber of claim 15, wherein said resin is selected from the groupconsisting of polyamide epichlorohydrin adduct, urea or melamineformaldehyde.
 17. The fiber of claim 16, wherein said resin is polyamideepichlorohydrin adduct.
 18. The fiber of claim 14 prepared according tothe method of claim
 1. 19. The fiber of claim 14, wherein said cellulosefiber is selected from the group consisting of southern softwood kraft,northern softwood kraft, tropical hardwood kraft, northern softwoodsulfite, southern softwood sulfite, or cotton linter cellulose.
 20. Thefiber of claim 14 prepared according to claim
 1. 21. The fiber of claim14 mercerized in the presence of a swelling agent.
 22. The fiber ofclaim 21, wherein said swelling agent is sodium hydroxide or potassiumhydroxide.
 23. The fiber of claim 21, wherein said swelling agent issodium hydroxide.
 24. The fiber of claim 22, wherein said swelling agentis present at a concentration of at least about 80 grams/liter.
 25. Thefiber of claim 21, wherein said fiber is mercerized at a temperature ofat least 20° C.
 26. A method for preparing resin-treated mercerizedfibers comprising the steps of: (a) introducing mercerizing strengthcaustic to a high consistency cellulose pulp to produce a lowconsistency slurry; (b) neutralizing said mercerized cellulose pulp; (c)introducing to the pulp a resin is selected from the group consisting ofpolyamide epichlorohydrin adduct, urea, melamine formaldehyde, andmixtures thereof, in an amount of between 0.1 to 10 wt. % of dry pulp,and adjusting the pH of the pulp to between about 5.5 and 6.5; and (d)drying the pulp with the application of heat to obtain individualized,cured fibers.